Engine controllers control many engine operational parameters such as air charge, fuel charge, exhaust gas recirculation, fuel vapor recovery, ignition timing, camshaft timing, valve timing, and so on. These parameters are controlled to achieve desired engine power while minimizing emissions.
Control of these parameters requires knowledge of camshaft position. Typically, a toothed wheel with one or more missing teeth is positioned on the camshaft and a detection of the passing teeth determines camshaft position.
Engine controls are more complicated in vehicles equipped with variable cam timing. Camshafts are driven by belt or chain couplings to the crankshaft. For engines equipped with variable cam timing (VCT), the timing or phase of the camshaft varies relative to the crankshaft. An electric motor or hydraulic actuator turns the camshaft relative to the crankshaft.
When an engine is being cranked during an engine start, detection of the passing cam teeth, or other detection method, may not provide accurate cam position measurement, which usually requires detection of several rising and falling edges. Nevertheless, a VCT actuator may phase the camshaft during cranking using position and/or velocity measurements obtained internally (e.g., using an encoder built into the actuator), and a default cam position relative to the crankshaft.
The inventors herein have recognized an issue with the approach identified above. Specifically, the default relative position between the camshaft and the crankshaft may become increasingly inaccurate over time, as wear occurs in various couplings between the camshaft and the crankshaft (e.g., from the crankshaft to a VCT actuator input shaft, from the actuator input shaft to a motor stator, from a motor rotor shaft to the camshaft, etc.). Consequently, the engine controller may not accurately determine cam position during engine cranking. Without accurately knowing cam position, any estimate of air charge in the combustion chamber may be in error and consequently the air/fuel charge may be inaccurate, possibly resulting in longer engine starts and higher emissions. Similar issues may occur with other controlled operating parameters.
The inventors herein have solved the above issues with a method of operating a camshaft, comprising in one example the following: adjusting the camshaft based on a desired camshaft position, the desired camshaft position determined based on a camshaft position indicated by a camshaft sensor and a camshaft position indicated by a camshaft actuator. By utilizing both camshaft positions indicated by the camshaft sensor and by the camshaft actuator, inaccuracy in camshaft positioning, particularly during engine cranking, may be mitigated. After engine cranking, when the engine has started, subsequently determined desired camshaft positions may be corrected based on differences between camshaft positions indicated by the camshaft sensor and those indicated by the camshaft actuator. Thus, the technical effect is achieved.
In one typical example, the camshaft is adjusted during engine cranking.
In another example, if output from the camshaft sensor is not sufficiently accurate, the camshaft position indicated by the camshaft sensor is a previously recorded camshaft position determined when output from the camshaft sensor was sufficiently accurate.
In yet another example, adjusting the camshaft includes sending the desired camshaft position from an engine controller to a motor controller of the camshaft actuator.
In still another example, the camshaft actuator is an electric motor.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.